Certain vehicles require that the vehicle body be a specific height above the ground to maintain proper handling and operation, as specified by the vehicle manufacturer. This height is referred to as the ride height of the vehicle. To maintain the proper ride height of the vehicle throughout its lifespan, the height is typically measured at the time of a wheel alignment.
A current technique for measuring ride height involves wheel alignment equipment referred to as machine vision aligners or “visual aligners.” Visual aligners use optical targets attached to each vehicle wheel. The targets are imaged by cameras, and these individual images are used to calculate the vehicle wheel alignment angles. Such conventional visual aligners are described in U.S. Pat. Nos. 5,724,743; 5,809,658; 5,535,522; and 6,968,282, which are hereby incorporated by reference in their entirety.
Conventionally, a specific type of target is used to measure the ride height of a vehicle. It is referred to as a “TIP” target, and is shown in FIG. 1. It consists of an optical target 105 fixed to the end of a pointer rod 100. Target 105 has fiducial marks (not shown) on its surface, such as circles or other shapes, similar to conventional wheel targets used with visual aligners. The tip of the rod 100 is positioned by a user on specific points of a vehicle as specified by the visual aligner software. The aligner's cameras read the target 105's location and orientation, and this image is used by the software to determine the height of the vehicle off the ground. Any time the user wants to know how alignment adjustments have affected the height of the vehicle, they must repeat this procedure.
As more vehicles become dependent on their ride height to produce a proper wheel alignment, a need has arisen for a way of dynamically measuring the ride height while the wheel alignment is being performed. To effectively do this with a visual aligner system, targets are mounted on each of the four wheel wells of the vehicle. This allows a visual aligner to dynamically track and display to the user how the changes being made to the wheel alignment are affecting the ride height of the vehicle. The user is thereby able to adjust the vehicle alignment and maintain the OEM specified ride height with less redundancy and in less time.
A critical problem with this approach occurs when the user places the ride height target on the wheel well. It is difficult to have a reference to the correct point of measurement of the wheel well, because wheel wells have curves which make it difficult to index the bottom of them with the ride height target assembly. One solution is to put a level vial on the ride height target assembly, as described in U.S. Pat. No. 8,587,791. However, the aligner cannot confirm that the target is in fact level, so if the user is not careful, the aligner will measure the ride height incorrectly. Additionally, if the target should slip during the alignment procedure, or if it is not placed directly above the center of the wheels, it will not be at the correct place in the arc of the wheel well and the aligner will not give correct ride height measurements, because the aligner does not know the target is incorrectly placed.
A better solution is required to ensure the ride height target is mounted level, that the ride height target does not move or slip during the measurement process, and that the target is in the center of the wheel well directly above the center of the wheel.